PHP equivalent javascript >>> shift right with zero fill bitwise operators?

Question

May I know how can I do PHP >>> ? Such operators is not available in PHP, but is available in Javascript.

I just managed to discover a function as follow:

function zeroFill($a, $b) 
{ 
    $z = hexdec(80000000); 
        if ($z & $a) 
        { 
            $a = ($a>>1); 
            $a &= (~$z); 
            $a |= 0x40000000; 
            $a = ($a>>($b-1)); 
        } 
        else 
        { 
            $a = ($a>>$b); 
        } 
        return $a; 
}

but unfortunately, it doesn't work perfectly.

EG: -1149025787 >>> 0 Javascript returns 3145941509 PHP zeroFill() return 0

I imagine you've seen: http://php.net/manual/en/language.operators.bitwise.php — maček, Apr 15 '10 at 01:20
@incrediment: Out of nearly hundred result only 1 is incorrect: -1149025787 >>> 0 In javascript returns 3145941509 but in zeroFill() above, it just return 0. — neobie, Apr 15 '10 at 02:12

neo.peng · Answer 1 · 2018-06-21T06:07:50.110

9

/**
 * The >>> javascript operator in php x86_64
 * Usage: -1149025787 >>> 0 ---> rrr(-1149025787, 0) === 3145941509
 * @param int $v
 * @param int $n
 * @return int
 */
function rrr($v, $n)
{
    return ($v & 0xFFFFFFFF) >> ($n & 0x1F);
}

/**
 * The >> javascript operator in php x86_64
 * @param int $v
 * @param int $n
 * @return int
 */
function rr($v, $n)
{
    return ($v & 0x80000000 ? $v | 0xFFFFFFFF00000000 : $v & 0xFFFFFFFF) >> ($n & 0x1F);
}


/**
 * The << javascript operator in php x86_64
 * @param int $v
 * @param int $n
 * @return int
 */
function ll($v, $n)
{
    return ($t = ($v & 0xFFFFFFFF) << ($n & 0x1F)) & 0x80000000 ? $t | 0xFFFFFFFF00000000 : $t & 0xFFFFFFFF;
}

Enjoy it.

edited Jun 21 '18 at 06:07

answered Jun 21 '18 at 03:06

neo.peng

91
1
2

Next level stuff – Martin Zvarík Sep 21 '21 at 22:00
The RRR function doesn't work in some cases as expected. – Martin Zvarík Oct 15 '21 at 12:33

score 5 · Answer 2 · answered Dec 03 '14 at 03:47

5

Twice as fast for negative numbers as using the decimal-binary conversions

function zerofill($a,$b) { 
    if($a>=0) return $a>>$b;
    if($b==0) return (($a>>1)&0x7fffffff)*2+(($a>>$b)&1);
    return ((~$a)>>$b)^(0x7fffffff>>($b-1));

answered Dec 03 '14 at 03:47

M '431

106
1
5

score 3 · Answer 3 · edited Jun 21 '18 at 06:18

3

I've researched a lot on this, collected more than 11 versions from StackOverflow and open-source projects, none of them worked. But finally, I found the solution.

For more details, live demo, tests and examples check my question and answer:
Unsigned Right Shift / Zero-fill Right Shift in PHP (Java/JavaScript equivalent)

function unsignedRightShift($a, $b) {
    if ($b >= 32 || $b < -32) {
        $m = (int)($b/32);
        $b = $b-($m*32);
    }

    if ($b < 0) {
        $b = 32 + $b;
    }

    if ($b == 0) {
        return (($a>>1)&0x7fffffff)*2+(($a>>$b)&1);
    }

    if ($a < 0) 
    { 
        $a = ($a >> 1); 
        $a &= 0x7fffffff; 
        $a |= 0x40000000; 
        $a = ($a >> ($b - 1)); 
    } else { 
        $a = ($a >> $b); 
    }

    return $a; 
}

edited Jun 21 '18 at 06:18

king_nak

11,313
33
58

answered Apr 12 '17 at 04:19

frzsombor

2,274
1
22
40

@king_nak Thanks for the edit! Can you please share the reasons of it? Is it just for making it more consistent or anything related to safety or accuracy? – frzsombor Jun 21 '18 at 08:59
1

It is just for clarity and consistency. 2147483647 is quite obfuscated for me, but with 0x7FFFFFFF it is clear that all bits except the MSB are set – king_nak Jun 21 '18 at 09:21

score 2 · Accepted Answer · answered Apr 15 '10 at 06:17

I studied around the webs and come out with my own zerofill function, base on the explanation given. This method works for my program.

Have a look:

function zeroFill($a,$b) {
    if ($a >= 0) { 
        return bindec(decbin($a>>$b)); //simply right shift for positive number
    }

    $bin = decbin($a>>$b);

    $bin = substr($bin, $b); // zero fill on the left side

    $o = bindec($bin);
    return $o;
}

score 2 · Answer 5 · answered Feb 13 '15 at 23:44

2

For both 32-bit (PHP_INT_SIZE == 4) and 64-bit integers (PHP_INT_SIZE == 8):

function SHR
($x, $c)
{
    $x = intval ($x); // Because 13.5 >> 0 returns 13. We follow.

    $nmaxBits = PHP_INT_SIZE * 8;
    $c %= $nmaxBits;

    if ($c)
        return $x >> $c & ~ (-1 << $nmaxBits - $c);
    else
        return $x;
}

answered Feb 13 '15 at 23:44

MagnificentImbecil

21
1

doesn't work with `SHR(-1149025787,0)`, expected 3145941509, got -1149025787 – hanshenrik Sep 20 '18 at 17:51

score 1 · Answer 6 · answered Apr 15 '10 at 06:28

1

Your function doesn't work because when $b == 0, the expression

$a >> -1

will be evaluated, which returns 0.

Assuming 32-bit machines, you can add a special case:

if ($z & $a) {
  if ($b == 0)
    return $a + 0x100000000;
  else {
    ...

answered Apr 15 '10 at 06:28

kennytm

510,854
105
1,084
1,005

score 1 · Answer 7 · answered Jan 17 '11 at 04:41

Not sure if this works for php, I've manage to get it to work with C#.

int a, b, result;
//Instead of 
result = a >>> b;
//I do
result = (int)((uint)a >> b);

I found that out by debugging into the code that uses >>> comparing it with C# version of the code I converted from javascript. While trying out with b = 0, and using a scientific calculator to see the different hex/dec result of >> and >>> produce by javascript. When a is negative, >>> actually makes aa as unsigned.

Not sure if that works for all scenario, but for my case the >>> is for md5 hashing. Being able to produce similar output, I'm quite satisfied with the result.

Hope that helps

score 0 · Answer 8 · answered Aug 16 '13 at 22:59

0

This works for me

function RRR($a, $b){
    return (int)((float)$a/pow(2,(int)$b));
}

answered Aug 16 '13 at 22:59

Vitim.us

20,746
15
92
109

In some cases this doesn't work – Martin Zvarík Oct 15 '21 at 12:32

PHP equivalent javascript >>> shift right with zero fill bitwise operators?

8 Answers8

Linked